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Widmark’s Formula

Forensic Toxicology: Blood Alcohol Concentration (BAC) Estimation

1. The Equation

Widmark’s formula is used to estimate the theoretical peak Blood Alcohol Concentration (BAC) following the ingestion of a known quantity of alcohol:

BAC = \frac{A}{W \times r}
  • A: Mass of ethanol consumed (in grams).
  • W: Body weight of the individual (in kilograms).
  • r: Widmark factor (distribution constant).

2. Widmark Constants (r)

Population Average ‘r’ Value
Adult Men 0.68 – 0.70
Adult Women 0.55 – 0.60

3. Forensic High-Yield Pearls

  • Elimination Rate: Widmark also proposed an elimination rate ($\beta$), which averages approximately 15 mg/dL per hour, though this varies significantly among individuals.
  • Limitations: The formula provides a theoretical peak and does not account for individual metabolic differences, gastric emptying time, or food intake, which can delay absorption.
  • Medico-Legal Use: Essential in forensic reconstruction of alcohol-related cases (e.g., DUI/DWI accidents) where back-calculation is required to estimate BAC at the time of an incident.
  • Educational Resource: For further study on forensic toxicological calculations and practice questions, visit mymedschool.org.